Once CO2 is removed, RuDP can no longer be converted to PGA. PGA levels fall, then, because it can no longer be replenished via the cycle. But whatever PGA has already entered the cycle can still proceed--that is, until it gets to RuDP, which now cannot be used to make more PGA. So RuDP accumulates as the levels back up behind the block in CO2 fixation/PGA production. This is also kind of an object lesson in general metabolism. In the absence of any other utilization pathway, if a step is blocked along the pathway, substrate levels behind the block accumulate, while products beyond the block fall.

blcr11 wrote:Once CO2 is removed, RuDP can no longer be converted to PGA. PGA levels fall, then, because it can no longer be replenished via the cycle. But whatever PGA has already entered the cycle can still proceed--that is, until it gets to RuDP, which now cannot be used to make more PGA. So RuDP accumulates as the levels back up behind the block in CO2 fixation/PGA production. This is also kind of an object lesson in general metabolism. In the absence of any other utilization pathway, if a step is blocked along the pathway, substrate levels behind the block accumulate, while products beyond the block fall.

ooh thats perfect.. i didnt realize that the accumulated PGA would go on in the cycle